The Porto 3.5 theme uses the same CodeMirror editor as the Simple Custom CSS & JS plugin. The theme’s CodeMirror version of the editor is loaded on the “Edit Custom CSS” page and that version doesn’t have the “autocomplete” or the “find” functionality.
Note that this issues shows up only in the older versions of Porto. The 3.5 version is already more than 4 years old. Any Porto theme after 4.4.0 version (released May 2018) will not have this issue with the “autocomplete” and “find” functionality in the Simple Custom CSS and JS plugin.
If you want to fix this issue on your website, then you can edit the functions.php file in your theme’s folder and add the following two lines:
$screen = get_current_screen();
if ( $screen->post_type === 'custom-css-js' ) return;
right after the function porto_admin_scripts() {
line. On the Porto 3.6.2 version that would be after the line 399.